The invention relates to communications in general and to the recovery of supplemental information encoded into the primary information transmitted from a source to a receiver.
Historically, several methods have been used to transmit embedded data along with a carrier signal, such as a radio or television signal. In one approach, data is included in parts of the signal that do not interfere with the perception of the signal by a human receiving it. One approach is to use the vertical blanking interval (VBI) in television transmissions to transmit supplementary data. In this approach, a decoder device is typically attached to the receiver to provide accurate synchronization with the incoming transmitted signal.
A spread spectrum technique is another approach used to embed supplementary data in a transmitted signal. Traditionally, analog techniques have been used to decode the supplementary data encoded using a spread spectrum technique. In general, synchronization of the local code generator with the received code can be performed with an analog correlator. Depending on the frequency used and the application requirements, the synchronization can be a time consuming operation when performed by the analog correlator. The operation involves shifting the local code and computing its correlation with the received code, and repeating this process, typically many times, until the correlation is above a threshold.
In one approach to transmitting embedded data, the embedded data is encoded using frequency shift keying of bits at a low signal level. However, mixing can occur between the data frequencies and 60 Hz sampling of a television signal, producing lower frequencies that are detectable by humans.
The present invention overcomes these shortcomings.
One object of the invention is to produce a data embedding system that does not require a decoder attached to the receiving device. Another object is to embed the data without side effects detectable by the human perceiving the transmission. A further object of the invention is to shorten the time frame required for synchronization between the received signal and a local reference signal.
The invention relates to a method for encoding a second signal within the transmission of a first signal The method includes the steps of providing the first signal, providing the second signal, modulating the second signal utilizing a spread spectrum technique to form a code modulated signal, and modulating a carrier signal with the first signal and the code modulated signal.
The invention also relates to a method for transmitting a second signal within the transmission of a first signal. The method includes the steps of providing the first signal, providing the second signal, modulating the second signal with a spread spectrum technique to form a code modulated signal, modulating a carrier signal with the first signal and the code modulated signal, transmitting the modulated carrier signal, receiving the modulated carrier signal, demodulating the carrier signal to recover the first signal and the code modulated signal, separating the first signal from the code modulated signal, and demodulating the code modulated signal to recover the second signal. The spread spectrum technique used is a direct sequence technique, a frequency hopping technique, or a hybrid technique.
In one embodiment the first signal is a television video image and the recovered first signal and code modulated signal includes the television video image and a video representation of the second signal. In this embodiment, the step of separating the first signal from the code modulated signal includes the step of removing the television image.
In another embodiment the first signal is an audio signal and the recovered first signal and code modulated signal includes the audio signal and an audio representation of the second signal.
The invention also relates to an apparatus for extracting a second signal encoded in a first video signal. The apparatus includes a first photodiode, a second photodiode and a difference amplifier having an output terminal and having a first input terminal in electrical communication with the first photodiode and a second input terminal in electrical communication with the second photodiode. The apparatus also includes a code generator utilizing a spread spectrum technique and having an input terminal and an output terminal, a multiplier having an output terminal and having a first input terminal in electrical communication with the output terminal of the difference amplifier and a second input terminal in electrical communication with the output terminal of the code generator, and an integrator having an output terminal and having an input terminal in electrical communication with the output terminal of the multiplier. The apparatus further includes a code search synchronizer having a first input terminal in electrical communication with the output terminal of the integrator, having an output terminal in electrical communication with the input terminal of the code generator, and having a second input terminal. The apparatus further includes a processor having a first input terminal in electrical communication with the output of the integrator and having a first output terminal in electrical communication with the second input terminal of the code search synchronizer.
The first photodiode is configured to view the second signal encoded in the first video signal and the second photodiode is configured to provide a dark current threshold. The spread spectrum technique is a direct sequence technique, a frequency hopping technique, or a hybrid technique.
In another embodiment, the apparatus includes an output device having an input terminal, wherein the processor has an output terminal in electrical communication with the output terminal of the output device. The output device produces an output signal in response to the second signal from the processor.
The invention also relates to a system for transmitting and extracting a second signal encoded in a first video signal. The system includes a transmission system including a video signal source providing the first video signal at a first output terminal, a second signal source providing the second signal at a first output terminal, a code generator providing a code at a first output, a code modulator having an output terminal and a first input terminal in electrical communication with the output terminal of the second signal source and having a second input terminal in electrical communications with the output terminal of the code generator, an adder having an output and a first input terminal in electrical communication with the first output terminal of the video signal source and a second input in electrical communication with the output terminal of the code modulator, and a transmitter having an input terminal in electrical communication with the output terminal of the adder. The system further includes a television receiver having a television screen and a decoder including a first photodiode, a second photodiode, and a difference amplifier having an output terminal and having a first input terminal in electrical communication with the first photodiode and a second input terminal in electrical communication with the second photodiode. The decoder also includes a code generator having an input terminal and an output terminal, a multiplier having an output terminal and having a first input terminal in electrical communications with the output terminal of the difference amplifier and a second input terminal in electrical communication with the output terminal of the code generator. The decoder also includes an integrator having an output terminal and having an input terminal in electrical communication with the output terminal of the multiplier, a code search synchronizer having a first input terminal in electrical communication with the output terminal of the integrator, having an output terminal in electrical communication with the input terminal of the code generator and having a second input terminal, and having a processor having a first input terminal in electrical communication with the output of the integrator and having a first output terminal in electrical communication with the second input terminal of the code search synchronizer. The first photodiode is configured to view the television screen and at least one of the code generator and the code modulator utilizes a spread spectrum technique including a direct sequence technique, a frequency hopping technique, or a hybrid technique.
The invention also relates to an apparatus for extracting a second signal encoded in a first audio signal including a first audiodetector, an audio amplifier, an analog automatic gain control, a power detection circuit, a code generator, a multiplier, an integrator, a code search synchronizer, and a processor. The audio amplifier includes a first input terminal in electrical communication with said first audiodetector and an output terminal. The analog automatic gain control includes an input terminal in electrical communication with the output terminal of the audio amplifier, an output terminal and a gain control terminal. The power detection circuit includes an input terminal in electrical communication with the output terminal of the audio amplifier and an output terminal in electrical communication with the gain control terminal of the automatic gain control circuit. The code generator includes an input terminal and an output terminal and utilizes a spread spectrum technique. The multiplier includes a first input terminal in electrical communications with the output terminal of the automatic gain control circuit, a second input terminal in electrical communication with the output terminal of the code generator, and an output terminal, The integrator includes an input terminal in electrical communication with the output terminal of the multiplier and an output terminal. The code search synchronizer includes a first input terminal in electrical communication with the output terminal of the integrator, an output terminal in electrical communication with the input terminal of the code generator and a second input terminal. The processor includes a first input terminal in electrical communication with the output of the integrator and a first output terminal in electrical communication with the second input terminal of the code search synchronizer.
The invention also relates to a system for transmitting and extracting a second signal encoded in a first audio signal including a transmission system, an audioreceiver, and a decoder. The transmission system includes a audio signal source, a second signal source, a code generator, a code modulator, an adder, and a transmitter. The audio signal source provides the first audio signal at a first output terminal. The second signal source provides the second signal at a first output terminal. The code generator provides a code at a first output. The code modulator includes an output terminal and a first input terminal in electrical communication with the output terminal of the second signal source and a second input terminal in electrical communication with the output terminal of the code generator. The adder includes an output and a first input terminal in electrical communication with the first output terminal of the audio signal source and a second input in electrical communication with the output terminal of the code modulator. The transmitter includes an input terminal in electrical communication with the output terminal of the adder. The audioreceiver includes a sound generator. The decoder includes a first audiodetector, an audio amplifier, an analog automatic gain control, a power detection circuit, a code generator, a multiplier, an integrator, a code search synchronizer, and a processor. The audio amplifier includes a first input terminal in electrical communication with the first audiodetector and an output terminal The analog automatic gain control includes an input terminal in electrical communication with the output terminal of the audio amplifier, an output terminal and a gain control terminal. The power detection circuit includes an input terminal in electrical communication with the output terminal of the audio amplifier and an output terminal in electrical communication with the gain control terminal of the automatic gain control circuit. The code generator includes an input terminal and an output terminal, and utilizes a spread spectrum technique. The multiplier includes a first input terminal in electrical communication with the output terminal of the automatic gain control circuit, a second input terminal in electrical communication with the output terminal of the code generator and an output terminal. The integrator includes an input terminal in electrical communication with the output terminal of the multiplier and an output terminal. The code search synchronizer includes a first input terminal in electrical communication with the output terminal of the integrator, an output terminal in electrical communication with the input terminal of the code generator and a second input terminal. The processor includes a first input terminal in electrical communication with the output of the integrator and a first output terminal in electrical communication with the second input terminal of the code search synchronizer. The first audiodetector is configured to hear sound generated by the sound generator. The code generator and/or the code modulator utilizes a spread spectrum technique.
The invention also relates to a method for synchronizing a reference code signal with a received signal comprising an embedded code. The method includes reversing the order of bits in the reference code signal to produce a reversed code signal, performing a transform on the reversed code signal to produce a transformed reversed code signal, performing the transform on the received signal to produce a transformed received signal, processing the transformed reversed code signal and the transformed received signal to produce an intermediate signal, performing an inverse of the transform on the intermediate signal to produce a correlation signal, determining a peak value in the correlation signal, determining a wait value from the peak value and a time period to wait based on the wait value, and waiting for the time period to synchronize the embedded code in the received signal with the reference code signal.
In a further embodiment, the invention relates to a method for synchronizing a reference code signal with a received signal comprising an embedded code using a sampling approach. The method includes the steps of sampling the received signal to produce a sample signal, storing the sample in a memory, shifting the reference code by a predetermined increment to produce a shifted reference code, retrieving the sample signal from the memory, and multiplying the shifted reference code and the sample signal to produce an intermediate signal. The method further includes accumulating the intermediate signal, accumulating a plurality of intermediate signals, determining a peak value for the sample signal from the accumulated results, determining a wait value from the peak value, determining a time period from the wait value, and waiting for the time period while receiving the received signal to synchronize the embedded code in the received signal with the reference code signal.